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<h2 id="Summary" name="Summary">概述</h2>
<p><code><strong>Math.SQRT1_2</strong></code> 属性表示 1/2 的平方根，约为 0.707：</p>
<p><math display="block"><semantics><mrow><mstyle mathvariant="monospace"><mi>Math.SQRT1_2</mi></mstyle><mo>=</mo><msqrt><mfrac><mn>1</mn><mn>2</mn></mfrac></msqrt><mo>=</mo><mfrac><mn>1</mn><msqrt><mn>2</mn></msqrt></mfrac><mo>≈</mo><mn>0.707</mn></mrow><annotation encoding="TeX">\mathtt{\mi{Math.SQRT1_2}} = \sqrt{\frac{1}{2}} = \frac{1}{\sqrt{2}} \approx 0.707</annotation></semantics></math></p>
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<th class="header" colspan="2"><code>Math.SQRT1_2</code> 属性的属性特性：</th>
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<td>writable</td>
<td>false</td>
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<td>enumerable</td>
<td>false</td>
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<td>configurable</td>
<td>false</td>
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<h2 id="Description" name="Description">描述</h2>
<p>由于 <code>SQRT1_2</code> 是 <code>Math</code> 对象的静态属性，所以应该像这样使用：<code>Math.SQRT1_2</code>，而不是作为你创建的 <code>Math</code> 实例的属性（<code>Math</code> 不是构造函数）。</p>
<h2 id="Examples" name="Examples">示例</h2>
<h3 id="Example:_Using_SQRT1_2" name="Example:_Using_SQRT1_2">例子：使用 <code>SQRT1_2</code></h3>
<p>下面的函数返回 1/2 的平方根：</p>
<pre><code class="language-js">function getRoot1_2() {
   return Math.SQRT1_2
}

getRoot1_2() // 0.7071067811865476</code></pre>
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<h2 id="规范">规范</h2>
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<th scope="col">规范版本</th>
<th scope="col">规范状态</th>
<th scope="col">注解</th>
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<td>ECMAScript 1st Edition. Implemented in JavaScript 1.0</td>
<td>Standard</td>
<td>Initial definition.</td>
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<td><a class="external" href="https://www.ecma-international.org/ecma-262/5.1/#sec-15.8.1.7" hreflang="en" lang="en" rel="noopener">ECMAScript 5.1 (ECMA-262)<br/><small lang="zh-CN">Math.SQRT1_2</small></a></td>
<td><span class="spec-Standard">Standard</span></td>
<td> </td>
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<td><a class="external" href="https://www.ecma-international.org/ecma-262/6.0/#sec-math.sqrt1_2" hreflang="en" lang="en" rel="noopener">ECMAScript 2015 (6th Edition, ECMA-262)<br/><small lang="zh-CN">Math.SQRT1_2</small></a></td>
<td><span class="spec-Standard">Standard</span></td>
<td> </td>
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<h2 id="浏览器兼容性">浏览器兼容性</h2>
<p></p><div class="blockIndicator warning"><strong><a class="external" href="https://github.com/mdn/browser-compat-data" rel="noopener">We're converting our compatibility data into a machine-readable JSON format</a></strong>.
            This compatibility table still uses the old format,
            because we haven't yet converted the data it contains.
            <strong><a class="new" href="/zh-CN/docs/MDN/Contribute/Structures/Compatibility_tables" rel="nofollow">Find out how you can help!</a></strong></div>
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<a id="AutoCompatibilityTable" name="AutoCompatibilityTable"></a>
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<li class="selected"><a>Desktop</a></li>
<li><a>Mobile</a></li>
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<th>Feature</th>
<th>Chrome</th>
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<th>Internet Explorer</th>
<th>Opera</th>
<th>Safari</th>
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<td>Basic support</td>
<td><span style="color: #888;" title="Please update this with the earliest version of support.">(Yes)</span></td>
<td><span style="color: #888;" title="Please update this with the earliest version of support.">(Yes)</span></td>
<td><span style="color: #888;" title="Please update this with the earliest version of support.">(Yes)</span></td>
<td><span style="color: #888;" title="Please update this with the earliest version of support.">(Yes)</span></td>
<td><span style="color: #888;" title="Please update this with the earliest version of support.">(Yes)</span></td>
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<th>Feature</th>
<th>Android</th>
<th>Chrome for Android</th>
<th>Firefox Mobile (Gecko)</th>
<th>IE Mobile</th>
<th>Opera Mobile</th>
<th>Safari Mobile</th>
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<td>Basic support</td>
<td><span style="color: #888;" title="Please update this with the earliest version of support.">(Yes)</span></td>
<td><span style="color: #888;" title="Please update this with the earliest version of support.">(Yes)</span></td>
<td><span style="color: #888;" title="Please update this with the earliest version of support.">(Yes)</span></td>
<td><span style="color: #888;" title="Please update this with the earliest version of support.">(Yes)</span></td>
<td><span style="color: #888;" title="Please update this with the earliest version of support.">(Yes)</span></td>
<td><span style="color: #888;" title="Please update this with the earliest version of support.">(Yes)</span></td>
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<h2 id="See_also" name="See_also">相关链接</h2>
<ul>
<li>The <a href="Reference/Global_Objects/Math" title="Math 是一个内置对象， 它具有数学常数和函数的属性和方法。不是一个函数对象。"><code>Math</code></a> object it belongs to.</li>
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